What vs. Which

You can use 'what' and 'which' interchangeably; however, there are some delicate differences between these two. Let us start learning it through this article.

"What" vs. "Which" in the English Grammar

What Are Their Main Differences?

The key difference between 'what' and 'which' relies on what they refer to. Actually, 'what' refers to an open set of options, while 'which' is used for a closed set.


Although, you can use 'what' and 'which' interchangeably, there are certain examples where only one of them can be correct.

Use What for Unlimited Answers and Which for Limited Answers

  • 'What':

is used to ask questions when there are lots of answers. For example, when you ask; 'What is your favorite color?' the person can name many different colors.

  • 'Which':

is used when the answers are fewer, so they are limited. For example, when you ask; 'Which of your children is going to ballet class?'

What is its name?

What do you need?

What do you do?

Which glass was mine?

Which finger do you feel pain in?

Which one is your father? the one with black shirts or the other?

Background Knowledge

Whenever you know something already, or you have knowledge about the choices in advance, 'which' is a better option to use.

Which president started the Vietnam war?

Which actor has won the most Oscars?

How They change the Whole Meaning

Since 'what' refers to more options than 'which' they can subtly change the whole meaning of the sentences. Look at the examples to be clarified.

What happened during world war II? (in a test)

Which happened during world war II? (in a test)

'What' and 'Which' as Relative Pronouns

  • 'Relative pronouns':

Whenever a relative pronoun, referring to actions and things, is required; we need the relative form of 'what', which is the word 'that', while the relative pronoun of 'which' is the term 'which'.

The house that is painted in blue looks different from the other ones.

The small animal which has thick long tail is a raccoon; not the one with the long neck.


'What', 'Which', or Both?

Whenever there are several options but not infinite choices, either 'what' or 'which' will work perfectly.

What flight are you taking to Chicago?

Which flight are you taking to Chicago?

What day is your wedding?

Which day is your wedding?


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